Several reports have suggested that genita mycoplasma may be involved in human infertility although the evidence is conflicting. The situation in regard to Chlamydia is even more unclear. Some studies utilizing tetracycline have caused infertile women to conceive, but again there are conflicting reports in this regard. Tetracycline could affect a variety of microorganisms including Chlamydia and genital mycoplasmas. To our knowledge no extensive study of Chlamydia infection in infertile women has been carried out. For this reason we propose investigating infertile women for the presence of Chlamydia infecton as well as genital mycoplasma carriage. The study would be carried out by utilizing women who are intensively investigated for infertility. Women with no demonstrable cause for their infertility (explainable) would constitute the controls. Evidence for Chlamydia infection would be determined by culture and local and serum antibody studies. Evidence for mycoplasma carriage would be carried out utilizing culture and serological techniques. Those patients with explainable infertility would be divided into groups based on the cause of their infertility. Thus, evidence for infection with Chlamydia and mycoplasmas in the idiopathic group would be compared with evidence of infection in groups of patients with endocrine, cervical, tubal, male and mixed causes for their infertility. Suitable statistical methods would be employed to insure the incomparability of these groups.